Lateral power metal-oxide semiconductor field-effect transistors (MOSFETs) are valuable components in many power circuits, for example, in those that are included in portable power management products, personal computer peripherals, and automotive devices. The benefit of lateral power MOSFETs include generally high switching speeds and a relatively low on-resistance.
Improvements to packing density and on-resistance have been achieved by implementing a lateral MOSFET with a trench that has a gate, channel, and drift region along a sidewall of the trench. A lateral trench MOSFET, referred to as a trench-type lateral MOSFET, can provide a significant reduction in a lateral dimension, such as a cell pitch, in comparison to a non-trench-based lateral MOSFET. This reduction in cell pitch tends to lower the on-resistance of the transistor.
FIGS. 1A and 1B illustrate conventional trench-type lateral MOSFETS. The chief difference between the MOSFETS in FIGS. 1A and 1B is that an n-drift region is implanted in FIG. 1A and is formed from an epitaxial layer in FIG. 1B. The operation of the devices is substantially the same and will be described coincidentally. In particular, the MOSFETS in FIGS. 1A and 1B include a gate, channel, and a drift region (e.g., n-drain region in FIGS. 1A and n-epi layer in FIG. 1B) formed along a sidewall of a trench, and a source region adjacent to the channel and in contact with a surface-located source contact. Current flow through the channel can proceed from the source contact at the surface of the device, through the channel, to drift and drain regions at the bottom of the trench, and into a drain electrode residing in the trench along with the gate.
When in a blocking mode, the drift region can sustain a portion of an applied voltage. Structural dimensions and doping levels of portions of a lateral trench MOSFET can be selected to provide a particular breakdown voltage. For example, the trench depth can be increased to increase breakdown voltage.
In contrast to a lateral trench MOSFET, a vertical trench MOSFET can have a vertically disposed drain, with a drain contact on a backside of a die. A lateral trench MOSFET, however, has all terminal connections available at the top surface of a die, and typically can be more readily integrated with other components in an integrated circuit.